Muscle Mustangs & Fast Fords
Ford Shelby GT500 Modifications - Shelby Bolt-On Bonanza, Part 2 - Tech
The GT500 Gets Off Its High Horse And Into High Gear With A Few More Bolt-Ons.
When last we left you, we had spent a day at the track, taking a bone-stock Shelby GT500 into the 11-second zone with a few basic bolt-ons. Giddy with success, we spent yet another day wrenching on Ford's new supercar in search of more bolt-on happiness.
Before we delve into Part 2's results, let's rehash our efforts from Part 1. We cruised the 800-mile-old GT500 to MM&FF's resident drag-strip, Old Bridge Township Raceway Park, in scenic New Jersey. Once there, we made three baseline runs that would set the stage for the ensuing test. Bone stock, the GT500 recorded a best elapsed time of 12.38 seconds at 115 mph. At the end of that day, thanks to M&H Racemaster drag radials, a JDM custom tune uploaded into the ECM via an SCT Flash tuner, and a MagnaFlow after-cat exhaust system, the Shelby slammed into the 11-second zone, motoring down to an 11.78 with the speedometer (and the track's clock) reading 117 mph. The vehicle weight with driver was 4,080 pounds.
Just like the average car guy or girl, we wanted more. The bolt-ons we installed trackside in Part 1 showed the potential of not only the Shelby itself, but of the parts, too. If those modifications could pick up two ticks on the speedometer and drop almost 6-tenths of a second off the baseline elapsed time, what could a few more simple bolt-ons do to the 5.4-liter beast? Could we get this blown S197 into the 10-second zone with basic stuff? We couldn't conclusively answer that question without trying, so you can see the road we are going to travel down in Part 2 of this bolt-on bonanza. Cinch down the belts and get ready to ride.
For the second round of bolt-ons, we kept the previously installed parts on the car. We once again drove the car to Raceway Park under its own power and ran it on high-test, 93-octane pump gas. During the week, however, the Shelby graced the JDM Engineering shop as this edition's modifications were installed with the car on the lift. While the following modifications can be performed in your driveway or garage, having the car on the lift with the proper tools makes the job much easier and less time consuming.
Geared to Perfection
It's common knowledge that the solid-axle 8.8-inch rear that comes with the Shelby houses 3.31 gears. While the factory ring-and-pinion will get the job done on the highway, when you want to start shedding elapsed time, the 3.31 cogs are not the best choice. So, changing the gears in the rear was the first item on the checklist. Keep in mind two things when changing the ring-and-pinion gears, however. First, make sure you choose the correct gear ratio. There are many different ratios available, so the proper one is dependent upon application, driving style, and the modifications you have already made and are planning to make. Generally, factory Mustangs don't have enough rear gear ratio to maximize quarter-mile acceleration. Ford under-gears them to enhance fuel economy and engine life and to reduce NVH. These modular engines like to rev, though, and adding gear (numerically) will allow the engine to rev quicker, thus enhancing acceleration. For example, switching from the 3.31s to a set of 3.55s or 3.73s will undoubtedly help a stock Shelby while keeping it driveable. Those 4.88s might not be the best choice for your stock GT500, though. If at all possible, avoid the bottom-of-the-page syndrome and consult a tech person when ordering your ring-and-pinion. With most new Stangs ('05-up), 4.10s or 4.30s make a great choice.
Secondly, when changing the gears in the rear, you are required to recalibrate the speedometer. "If you do not change the calibration, the computer will record a wheel torque error," says JDM Engineering's Jim D'Amore. "This error occurs when the speedometer reading doesn't match the actual vehicle speed. If this happens, the error will cause the car to go into fail-safe mode. To avoid this, you absolutely need to get into the tune and recalibrate the speedometer."
In an effort to better utilize the power we found in Part 1, we decided to swap out the stock 3.31s for a new set of 4.30s from Ford Racing Performance Parts. The idea was to not only get the car to 60-foot better with the numerically higher gears, but also to keep the engine in the powerband while going down the track.
During Part 1, driver Evan Smith noted it was barely necessary to use Fourth gear to avoid hitting the rev limiter in Third. This last-minute gear change brought down the engine speed, which undoubtedly hurt performance. With that in mind, the 4.30 gears were the items of choice as they would not over-rev the car at the finish line, but enable the Shelby to stay within the power band. In most cases, optimal performance comes when the engine is near, or at, redline just as it crosses the finish line in Fourth gear.
One of the notable aspects of Part 1 was the problem surrounding the stock mass airflow sensor (also known as the mass air meter) of the Shelby and the accompanying airbox and inlet system. Like a normal Mustang GT, the Shelby has a mass air meter that is integrated in the inlet tube and the factory airbox, in which the air filter is contained. Unfortunately, with the custom tune that D'Amore loaded up in Part 1, the engine had increased in performance and reached the limit of the stock MAF sensor.
"The mass air meter needed to be changed because the stock unit was being pegged," D'Amore says. "The meter will register only 5 volts. Once it gets to that point, it pegs and sends a signal to the ECM. With this signal, the ECM interprets the car running in a lean state, and with the new Mustangs being a drive-by-wire system, the ECM closes the blades to the throttle body, thus cutting power.
To combat this, D'Amore had to create a MAF sensor to replace the stock piece. The JDM MAF sensor measures 116 mm, as opposed to the stock MAF sensor, which measures around 90 mm. In addition to the MAF sensor, D'Amore came up with a fresh-air intake kit. With the kit, he ditched the factory airbox and replaced it with an unshrouded high-flow K&N filter. He also unloaded the stock inlet tube for a smoothed inlet tube that promotes better airflow into the throttle body.
With the new MAF sensor, the tune needed to be reworked to take advantage of the increase in airflow into the engine and to make sure that no harm would come to the powerplant. "With the new mass air meter, I had to change the tune accordingly," D'Amore says. "I changed the mass air transfer functions along with the injector variables. A lot of what I changed in the tune is proprietary information, but overall, a lot of things within the tune had to be changed to not only make power but to keep the car driveable."
Shock it to Me, Baby!
As we detailed in Part 1, launching the car on stock tires was extremely difficult, and with the new M&H Racemaster drag radials, there was a fine line between bog, spin, and perfection on the launch pad. Additionally, Smith reported the GT500 had severe wheelhop when doing the burnout. With the power increases we were seeing and expecting from the Shelby, we realized that getting the car to leave hard and consistent would go a long way to helping us use the Shelby's newly found ponies. This meant a set of adjustable rear shocks was in order.
With the Mustang on the lift at the JDM shop, we had the stock rear shocks taken out and replaced with a pair of QA1 Stocker Star 12-way adjustable shocks. The QA1s feature deflective disc-valving technology and are billed to give you increased valving response, control, and consistency. The shock is composed of a 51/48-inch hard chrome piston that eliminates rod flex, and a forged aluminum body that is lightweight and durable. What mainly separates the QA1 shocks from the factory pieces are the QA1s' adjusta-bility. By looking at such things as vehicle weight, tire choice, transmission type, and other vari-ables, you can choose the shock setting that works best. The QA1s were an easy bolt-on, and while they would not add to the power level of the car, they would certainly help us in applying the power to the track surface.
Tracking the Monster
With everything bolted-on and ready to go, the Shelby made its way to the track for a performance evaluation of the new modifications. Filled with high-test and running on the drag radials, which were set at 16 psi, the same pressure we had them at in Part 1, Smitty swung behind the wheel and strapped on his skid lid. The air was better than it was for Part 1, so we figured the car would pick up a tenth based solely on the weather. In addition, the stiff headwind we experienced in Part 1 had moved around the compass, becoming a slight crosswind, which would have no effect on performance.
The QA1s were set with four clicks or turns from the full loose position for the first run, and after heating up the hides in the left lane burnout box, Smitty rolled up to the starting line. Keeping everything the same as the first test, he left the starting line at 4,500 rpm and recorded a 1.673 60-foot time, the best short time for the Shelby as of yet. Making each of the three gear changes at 6,500 rpm with the throttle planted wide open, he piloted the Shelby to an 11.246 at 124.01.
"The car spun a bit on the first run, but it accelerated and actually felt very good because it never pulled the engine back, it just went," Smitty reported. In addition, there was no nonsense in the burnout. To combat the slight spin, Shaun Lacko of JDM wiggled underneath the rearend and changed the shock settings, adding two clicks, thus tightening the shocks. This was done to slow the action of the rear on launch, which would control the "hit" at the tires and the rebound effect that can cause spin. By changing the setting to 6, a stiffer setting, the rearend of the car would not squat as easily. With the harder setting, we were trying to get the rearend to plant and stay planted, instead of planting and rebounding. With the car cooled down and the shocks adjusted, it was time for a second attempt at the quarter-mile.
This time, the car hooked extremely hard, causing it to bog down the motor. This hurt the short time, as the Shelby mustered only a 1.718 60-foot clocking. At the stripe, the speed was up slightly to 124.25, but the elapsed time fell off a bit as the Shelby ran an 11.294. After another cooldown period, Smitty attempted to leave a bit more aggressively, but the traction had gone away on the starting line in the left lane. In an effort to try and get a decent third run, we let the car cool back down after three aborted launches (all of which were not better than 1.70) and subsequently moved over to the right lane. Our plans were foiled slightly, though. The traction in the right-hand lane was much better than any-thing we had experienced in the left throughout the day. The extra bite once again caused the car to hook hard and bog, resulting in the worst 60-foot time of the day, a 1.721. At the quarter-mile mark, the scoreboards lit up to read an 11.37/123 mph pass, our slowest of the day.
Ending on the Right Foot
While the Shelby progressively slowed down in elapsed time from our first run of the day to the last, the elapsed time and speed gains with the new bolt-ons were enormous. With tire pressure the same as the first test, as well as launch and shift rpm, the Shelby ripped off a best e.t. of 11.246 seconds and a best speed of 124.25 mph. Even more impressive were the gains from the previous modification and those seen overall with all of the bolt-ons from the baseline effort.
From the previous modification, the gears, MAF sensor and accompanying fresh-air kit, and adjustable shocks lowered the Shelby's best e.t. by a sizeable 0.539 second, while terminal velocity went up almost seven markers. With all of the bolt-ons we have installed combined, the performance gains seen over the numbers laid down by the car when it was in stock trim is astounding. Overall, the seven different bolt-ons that have made their way onto the Shelby have shown a drop of 1.134 seconds in elapsed time and an increase of 9 mph on the speed chart. That's not just impressive; it blew us away.
If we had more time to play, however, we would have changed the rear shock setting and practiced our launches. Like any drag car, the key to quick elapsed times is in the launch. In the Shelby's case, it's tricky moving the 2-ton weight off the line quickly and consistently. Also, keep in mind our tester still has the stock front wheels, tires, and the front antiroll bar installed.
So what's in store for Part 3? Our twisted, psychotic minds are working overtime with ideas. We wanted to try and change blower pulleys in this installment, but a few trial runs on the dyno showed us some things weren't up to snuff. "On the dyno, the engine went lean at 5,800 rpm," D'Amore says. "It needs more fuel, and that will only come with an upgraded and improved fuel system and more tuning-and that is coming next." While we aren't psychics, we can see headers, boost, more fuel, and a 10-second time slip in this Shelby's future.
Another Tale of the Times
Part 1 was good, but Part 2 was better. In addition to the bolt-ons we threw on in Part 1, we added a few more in the second installment. Once again, the numbers don't lie. This beast is getting out of control, which is how we want it. Note: Differences are from the baseline run first and previously performed modifications second. Additionally, we are including all of the previously printed numbers from Part 1.
|Modification||Best ET/MPH||E.T. Difference||MPH Difference|
|Gears, Fresh-Air |
Kit w/116 mm
MAF and Tune,
|11.246/124.25 ||-1.134/-.539 ||+8.87/+6.94 |